The present invention relates to a viscous heater that genarates heat by shearing viscous fluid by rotor rotation in a heating chamber and transfers the heat to coolant circulating through a heat exchange chamber.
Automotive vehicles are generally equipped with hot water type heaters. A vehicle equipped with such a heater uses coolant to cool its engine. The coolant is supplied to a heater core and then heats the air in the passenger compartment.
It is difficult to maintain the coolant temperature above a certain level, for example 80.degree. C., in diesel engines and lean-burn engines, which generate less heat. In these cases, the hot water type heater does not supply enough heat for warming the passenger compartment.
To solve this problem, it has been proposed to provide a viscous fluid heater to heat the coolant. The viscous fluid heater has a heating chamber and a water jacket (heat exchange chamber), partitioned within a housing. The heater also has a drive shaft and a rotor driven by the engine. Viscous fluid, such as high viscosity silicone oil, is accommodated in the heating chamber and sheared by the rotor. The rotor generates heat by shearing the viscous fluid, and the resulting heat increases the temperature of the coolant circulating through the water jacket.
The temperature of the viscous fluid enclosed in the heating chamber increases as the engine speed increases without regard to the coolant temperature. Silicone oil is often used as the viscous fluid. Silicone oil is liable to deteriorate because of the heat and shearing when its temperature goes beyond, for example, 250.degree. C. When such deterioration occurs, the efficiency of heat generation by shearing viscous fluid goes down, and this degrades the heating capacity in the passenger compartment. Thus, it is necessary to take measures to prevent and deter the viscous fluid deterioration.